How do you get green skin after going into a pool and how do you get rid of it?

My little sister went into our pool for the entire day, almost, and came out with green line/ areas on her arms. Th enext day she went in again and came out with green on her legs. She tried to get it off with soap and water but it didn%26#039;t work. I also was in about the same amout of time and I%26#039;m not green at all.|||try rubbing areas with a little olive oil.Maybe it will just go on it%26#039;s own eventually.Next time she goes in try putting some barrier cream on her cheers